1. Field of the Invention
The present invention relates to map-updating-data creating methods, and map updating methods and apparatuses, and in particular, to a method for creating map-updating data for use in map updating in the background while performing navigation control, and a map updating method and apparatus.
2. Description of the Related Art
A navigation apparatus reads, from a recording medium such as a CD-ROM (compact-disk read-only memory), a DVD (digital versatile disc), or a hard disk, map data corresponding to the present position of a vehicle, and draws the read map data to display a map on a display screen. In addition, the navigation apparatus fixedly displays a vehicle mark at a predetermined position, and scrolls the displayed map in accordance with traveling of the vehicle. The map data includes (1) a road layer including node data, road link data, and intersection data, (2) a background layer for displaying objects on the map, and (3) a character layer for displaying municipality names, etc. A map image displayed on the display screen is generated based on the background layer and the character layer, and map matching and guidance-route searching are performed on the basis of the road layer. Additionally, the navigation apparatus has a route guidance function which searches for a guidance route from a place of departure to a destination and which displays the guidance route on the map, and a personal computer display function that displays predetermined POI (place of interest) marks on the map.
The map data recorded on the recording medium becomes obsolete with time because of a topographic data changes due to construction of a new road, etc., opening and closure of facilities, housing/land improvement, and other reasons. Accordingly, a technology (see, for example, Japanese Unexamined Patent Application Publication No. 2003-337027) of the related art has been proposed in which updated map data is stored in units of regions in a nonvolatile memory of a navigation apparatus, and navigation control is performed such that a map of a region whose map data has been updated is read from the nonvolatile memory and a region whose map data has not been updated is read from a recording medium (such as a CD-ROM). This technology performs writing the latest map data of regions (blocks) obtained by performing updating in units of meshes from a removable memory to a nonvolatile memory such as a hard disk, and checking, by referring to block management information, whether updated map data of all the meshes, which form the blocks, are stored in the nonvolatile memory. If the updated map data is not stored in the nonvolatile memory, map information is read from a recording medium (such as a CD-ROM). If the updated map data is stored in the nonvolatile memory, the updated map data stored is read and used to perform navigation control. Since, in this technology, it is necessary to perform the navigation control by using both the recording medium, such a CD-ROM or DVD, and the nonvolatile memory such as a hard disk, this technology has a problem in that the navigation control is complicated. In addition, this technology constantly needs a map recording medium, such as a CD-ROM or DVD, for navigation control. Thus, it is required that a music CD player and a DVD player be provided separately from a map playback device, so that a problem occurs in that necessary hardware has a large size.
Accordingly, a method (see, for example, Japanese Unexamined Patent Application Publication Nos. 2004-287705 and 2001-165675) has been proposed in which map data is stored in a map storage unit such as a hard disk, and, when the map data is altered, the map data on the hard disk is rewritten by the latest map data.
In Japanese Unexamined Patent Application Publication No. 2004-287705, a user can update old map data on a hard disk to new map data by acquiring a difference between the old map data and the new map data from a center, or purchasing an updating DVD containing the difference between the old map data and the new map data. This makes it possible to perform navigation control by using the map data on the hard disk, and enables a music-listening and video-viewing DVD player to be used as a DVD for maps. In addition, music and video can be enjoyed while performing navigation control.
FIG. 20 is a schematic illustration of creation of an updating DVD by a map-difference-data creating apparatus (not shown).
Since map data includes a large number of files, the map-difference-data creating apparatus creates difference data items DFD1 to DFDN by extracting, in units of files, a difference between old map file OFL in old version (version 1) and new map file NFL in new version (version 2). After that, the map-difference-data creating apparatus combines all the difference data items to create updating data, and creates an updating DVD 1 by writing the updating data in a DVD.
FIG. 21 is a block diagram showing an updating process of a navigation apparatus that uses the updating DVD 1 to update old map data on the hard disk to new map data. In the case of map updating, in the navigation apparatus, a hard disk (HD) reading unit 2 reads and inputs the old map file OFL in version 1 on a hard disk 3 to an updating unit 4, and a DVD playback unit 5 reads and inputs the difference data on the updating DVD 1 to the updating unit 4. The updating unit 4 creates the new map file in version 2 in units of files by using the difference data and the old map file OFL in version 1, and a hard disk (HD) writing unit 6 uses the new map file NFL to rewrite the old map file OLF.
In Japanese Unexamined Patent Application Publication No. 2001-165675, a map file to be updated and a map-updating date and time are recorded in a DVD-ROM. When a map file read from the DVD-ROM does not exist on the hard disk, the map file is written on the hard disk, and, when the map file exists, the map-updating dates and times of the map file read from the DVD-ROM and the map file on the hard disk are compared with each other. If the map-updating date and time of the map file on the hard disk is older, the map file on the hard disk is updated by using the map file read from the DVD-ROM.
However, the map updating in Japanese Unexamined Patent Application Publication No. 2004-287705 requires a long time of more than one or two hours. This is because time is taken by processing of creating a new map file based on an old map file and difference data and reading of the old map file. Accordingly, in the map updating, the vehicle needs to be left, with its engine running for the long time required for updating. Alternatively, after removing the hard disk, it is necessary to use a dedicated apparatus installed at a dealer to perform data rewriting for a long time. However, the map updating has a problem of inability to perform navigation control during the data rewriting.
In the map updating in Japanese Unexamined Patent Application Publication No. 2001-165675, although no use of difference data shortens the time required for the map updating compared with that in Japanese Unexamined Patent Application Publication No. 2004-287705, the amount of data is greater than that in the case of recording difference data since a map file to be updated is directly recorded on a DVD. Accordingly, all map files to be updated may not be recorded on a single DVD. The amount of map data at the present is approximately 15 gigabytes and the capacity of a DVD is 8.5 gigabytes. Thus, when more than half of the map files are altered, all the map files to be updated cannot be recorded on the single DVD. In this case, it is necessary to change DVDs during the map updating, so that a map updating operation is complicated. In addition, navigation control is impossible during the map updating.
In the technologies of the related art, disclosed in Japanese Unexamined Patent Application Publication Nos. 2004-287705 and 2001-165675, when updating old map data including a large number of map files, it is necessary to determine whether each map file has already been updated. In the above technologies, as shown in FIG. 22, a data version number (MT001) is assigned to map files 21 to 2N, and the data version number of all the map files 21 to 2N is incremented from MT001 to MT002 whenever map updating is performed. By referring to the data version number, it is determined whether each map file is the latest. The above determination requires processing in which, even for each map file whose map data is not to be updated, the map file is read from the hard disk and its version number is rewritten before being written on the hard disk. When considering that hundred thousand map files exist, a problem of a very long map updating time occurs.